MrrzyI haven't heard about the SAS but considering there role in the gulf war it is quite likely they are there quietly.
I've only heard Mr. Bush and Mr. Powell mention the use of "Special Forces" Delta Force is under the special forces command and as their role is freeing hostages it wouldn't be surprizng to see them deployed as well.
I expect that we soon will see special forces supplying coodination and communications to Northern Alliance troops.